Molded plastic containers, such as box-type containers having separately molded container and cover parts which are hinged together, are widely used. It has been recognized as desirable to provide a detachable latch member to effect closure between the cover and container in order to permit the latch to be replaced if it is damaged. In other words, if the latch arrangement is made as an integral part of the cover and/or container, damage to the latch requires replacement of the entire assembly; a detachable latch therefore greatly adds to the useful life of the container.
One prior art detachable latch is described in U.S. Pat. No. 3,730,576 to Schurman. This latch snap fits onto a container cover by means of an anchor bar on the cover which is laterally inserted into a slot on the latch. The anchor bar has enlarged working heads which fit through the latch slot such that the latch engages shank portions of reduced thickness behind the locking heads. During latching and unlatching operations severe stresses are placed on the reduced shank portions with the result that failure or rupture of the anchor bar occurs. Moreover, the latching mechanism itself relies on a locking tab snapping behind a latching shoulder. This snapping action, each time the container is opened and closed, provides a severe stress on the tab and shoulder, thereby resulting in a relatively short life for the latch. Importantly, since the latching shoulder is part of the container, rupture of the shoulder requires replacement of the entire container and thereby negates the intended advantage of providing a detachable latch. In addition, this tab-shoulder snapping arrangement renders it difficult to open the container quickly due to the fact that the snapping action is achieved with a relatively short tab; that is, the turning moment or torque applied to deform the tab in an opening operation is applied over the relatively short tab length so that little, if any, mechanical advantage is obtained. The required force to deform the tab and open the container is therefore relatively large.
Another prior art detachable latch is described in European Patent Office Publication 0002443 (Petit). In that publication, a latch is disclosed wherein the latch is detachably inserted into a slot in a container and projects upwardly from that slot to releasably engage a cover in a hook and notch engagement. Lateral clearance is provided in the slot so that the latch can be flexed to slide the hook away from the notch and release the cover for opening. This arrangement results in much less stress on the latch during opening and closing than is the case in the Schurman patent. However, the latch in Petit includes a projection which serves as the latch actuating mechanism and which resides in flush surface-to-surface or planar contact with the bottom edge of the cover. When the projection is pushed laterally to flex the latch and release the hook from the notch, friction between the flush surfaces of the latch projection and cover edge opposes lateral motion of the latch, thereby requiring a considerable applied force to effect opening of the container. Moreover, the hook and notch closure are slidably engaged and present frictional opposition to flexure of the latch during opening. Apart from adding to the required opening force, the friction between the hook and notch results in wear and tear of these two parts and leads to the premature failure of the latching mechanism.
It is therefore an object of the present invention to provide a detachable latch for a container-cover assembly which is easy to open and which is not subject to premature failure.
It is another object of the present invention to provide a detachable latch which fits a container in a manner such that frictional opposition to flexure of the latch member is minimized or non-existant.
It is still another object of the present invention to provide a detachable latch which, when operated, is not subject to stresses that may lead to failure.
Certain containers have covers on two sides; that is, the container body has two separate cover members hinged thereto on opposite sides. It is desirable to have a detachable latch which can independently latch both covers and which is devoid of the aforementioned disadvantages of prior art latches.
It is therefore an object of the present invention to provide a detachable latch which is capable of independently controlling two covers on opposite sides of a container and which is easy to operate and not subject to failure due to use.